Metal base hot-electron transistors (HETs) may be used for high-speed applications due to the fast electron transport speed and low resistive-capacitive (RC) delays across a metal base region of the transistor. However, some metal base HETs may exhibit low carrier transmission rate from the metal base into the semiconductor collector due to 1) the scattering inside the metal base, 2) the quantum reflection of carriers at the large potential step at the base-collector interface, and 3) the backward scattering by phonons inside the collector, which may cause the current gains of the metal base HETs to be less than unity.